1. Field of the Invention
The present invention relates to a four-cycle outboard motor.
2. Description of the Related Art
An engine of an outboard motor is mounted vertically so that the crankshaft is oriented in the vertical direction and comprises a combination of parts such as a crankcase, a cylinder block, and a cylinder head. If the engine is a four-cycle engine, an oil pan is installed at the bottom of the engine and a lubrication apparatus is installed at the bottom of the engine so as to lubricate the internal parts of the engine with lubricating oil that fills this oil pan and is drawn up by an oil pump.
An example of a conventional lubricating apparatus for an outboard motor is given in Japanese Laid-Open Patent Application H8-100614, where an oil pan is provided beneath the cylinder block and cylinder head, an oil pump is provided at the bottom of the cylinder head inside this oil pan and the oil pump is driven by a camshaft mounted inside the cylinder head.
Another example of a conventional lubricating apparatus for an outboard motor is given in Japanese Laid-Open Patent Application H5-26175. The lubricating apparatus includes an oil pump provided at a portion where the crankshaft sticks out from the lower side of the engine and wherein the oil pump is directly driven by the crankshaft.
When the oil pump is driven by a camshaft, a large oil pump is required in order to ensure the oil quantity and pressure needed for the engine because the camshaft rotates at half of the rotational speed of the crankshaft. Thus, both weight and cost are increased and the engine may not become so compact.
If the oil pump is driven directly by the crankshaft, the entire engine must be disposed at a higher position so that the oil pump does not interfere with a mounting apparatus for attaching the outboard motor to the boat. Thus, the outboard motor becomes larger and the center of gravity of the outboard motor becomes higher.
Interference between the oil pump and a timing chain, for example, is of particular concern with a type of outboard motor equipped with a camshaft drive mechanism at the bottom of the engine. In order to avoid the interference the outboard motor may become even larger.
The present invention was conceived in light of the above situation, and it is an object thereof to provide a four-cycle outboard motor that has a simple construction and a compact design.
The present invention satisfies the above-described needs by providing a four-cycle outboard motor having a crankshaft disposed substantially vertically within an engine, wherein rotation of this crankshaft is transmitted to a valve camshaft via a looped member disposed at the bottom of the engine, an oil pump disposed at the bottom of the engine but not along the axis of the crankshaft or the camshaft, and a tensioner of the looped member wherein either the oil pump or the tensioner is disposed inside the looped member in plan view and wherein the other is disposed outside the looped member in plan view.
The four-cycle outboard motor, according to the present invention, is further characterized in that the oil pump is at least partially disposed at the same height as the looped member such that the oil pump and the looped member are overlapped if viewed from the side.
The four-cycle outboard motor, according to the present invention, further comprises an oil pump drive apparatus provided to the camshaft wherein the oil pump is driven by the oil pump drive apparatus.
The four-cycle outboard motor, according to the present invention, is further characterized in that the oil pump drive apparatus is set to drive the oil pump at a higher rotational speed than the camshaft.
The present invention satisfies the above-described needs by providing a four-cycle outboard motor having a crankshaft disposed substantially vertically within a engine, wherein rotation of this crankshaft is transmitted to a valve camshaft via a looped member disposed at the bottom of the engine, and an oil pump disposed at the bottom of the engine, but not along the axis of the crankshaft or the camshaft, wherein the oil pump is driven by the looped member.
The present invention satisfies the above-described needs by providing a four-cycle outboard motor having a crankshaft disposed substantially vertically within an engine, wherein rotation of this crankshaft is transmitted to a valve camshaft via an idler shaft and two looped members disposed at the bottom of the engine, and an oil pump disposed at the bottom of the engine, wherein the oil pump is driven by the idler shaft.
The four-cycle outboard motor, according to the present invention, is further characterized in that the idler shaft is reduced in rotational speed.
The present invention satisfies the above-described needs by providing a four-cycle outboard motor having a crankshaft disposed substantially vertically within an engine, wherein rotation of this crankshaft is transmitted to a valve camshaft via a looped member disposed at the bottom of the engine, and an oil pump disposed at the bottom of the engine but not along the axis of the crankshaft or the camshaft, wherein the oil pump and a tensioner of the looped member are disposed outside of the looped member in plan view. Here, the plan view may include a horizontal cross section at the bottom of the engine.
The present invention satisfies the above-described needs by providing a four-cycle outboard motor having a drive shaft linked to a crankshaft, wherein the crankshaft and the drive shaft are disposed such that their axes are offset from each other, and wherein the axis of the drive shaft is disposed toward the rear away from the axis of the crankshaft, that is, the drive shaft axis is located closer to the cylinder head than the crankshaft axis.
The four-cycle outboard motor, according to the present invention, further comprises a sprocket or pulley for driving the camshaft provided coaxially with the drive shaft.
The present invention satisfies the above-described needs by providing a four-cycle outboard motor having a crankshaft disposed substantially vertically within an engine, wherein rotation of this crankshaft is transmitted to a valve camshaft via a looped member disposed at the bottom of the engine, a drive shaft linked to the crankshaft, wherein the crankshaft and the drive shaft are disposed such that their axes are offset from each other and wherein the axis of the drive shaft is disposed toward the rear away from the axis of the crankshaft (i.e., the drive shaft axis is located closer to the cylinder head than the crankshaft axis.), a sprocket or pulley for driving the camshaft provided coaxially with the drive shaft, and an oil pump disposed coaxially with the crankshaft, wherein this oil pump is driven by the crankshaft.
The four-cycle outboard motor, according to the present invention, further comprises an oil intake passage and an oil discharge passage provided inside the engine so as to extend from the opposite sides of the engine toward the oil pump substantially at a right angle to the axis of the cylinder in plan view. Here, the plan view in the present description may include a horizontal corss section projected on the same plane.